Cardioplegia is a commonly used technique for protecting a heart during open heart surgery in which cardioplegia solution is circulated through the heart tissues. The cardioplegia solution typically comprises a mixture of a medication, such as a potassium solution, and blood or a blood substitute. The cardioplegia solution stops the heart and provides oxygen to minimize damage to the heart. The selection of the particular content of the cardioplegia solution depends upon the particular physician. Moreover, it is becoming common to vary the content of the cardioplegia solution during the procedure.
Until this invention, the adjustable mixing of the components of a cardioplegia solution has been accomplished by providing separate pumps for each component. However, providing multiple pumps is expensive. Using multiple pumps also makes it difficult to make adjustments in the composition of the cardioplegia solution without changing the flow rate, or to change the flow rate without changing the composition of the solution.
The cardioplegia system of the present invention is adapted for mixing and administering cardioplegia medication and/or blood to a patient's heart during cardiopulmonary bypass surgery. The system comprises a tubing set, a positive displacement pump, and a mixing system. The tubing set includes a cardioplegia supply tube adopted for connection to a source of cardioplegia medication; a blood supply tube adopted for connection to a source of blood or blood substitute; and a cardioplegia administration tube connected to the cardioplegia and blood supply tubes, the cardioplegia administration tube being adapted to supply cardioplegia solution to the patient's heart.
The positive displacement pump is adapted for pumping fluid through the cardioplegia administration tube.
The mixing system controls the ratio of cardioplegia medication and blood or blood substitute in the cardioplegia administration tube. The mixing system comprises pinch valves for alternately-continually pinching the cardioplegia and blood supply tubes to close and open the cardioplegia and blood supply tubes such that only one of the cardioplegia and blood supply tubes is open at a time, and a controller for controlling the intervals during which the pinch valves are open with respect to each of the cardioplegia and blood supply tubes to control the ratio of the cardioplegia medication and blood or blood substitute administered through the cardioplegia administration tube.
The pinch valves can comprise a single double-acting solenoid valve that simultaneously allows one of the cardioplegia and blood supply tubes to open as it closes the other of the cardioplegia and blood supply tubes, or the pinch valves can comprise separate solenoid valves for each tube.
The tubing set may also include a recirculation tube, in which case the mixing system might also include a pinch valve for opening and closing the recirculation tube, the controller allowing only one of the cardioplegia supply, blood supply, and recirculation tubes to be open at any give time. A pressure transducer can monitor the pressure in the cardioplegia administration tube, and in response to a pressure exceeding a predetermined threshold, the controller can cause the fluid to open the recirculation tube pinch valve to simply recirculate. Also, the recirculation line provides a recirculation option to the surgeon who might wish to temporarily discontinue the administration of cardioplegia solution.
In a preferred embodiment of the invention, the tubing set can be provided as part of a cassette adapted to interfit with the control unit. The cassette would contain at least the cardioplegia and blood supply tubes, and preferably the recirculation tube as well. The cassette functions to hold these tubes, and position them properly with respect to the controller so that the pinch valves on the controller can operate to open and close the tubes.
The method of this invention provides for the mixing and administering cardioplegia medication and/or blood to a patient's heart during cardiopulmonary bypass surgery. Generally, this method comprises the steps of providing a tubing set, comprising a cardioplegia supply tube in fluid communication with a source of cardioplegia medication, a blood supply tube in fluid communication with a source of blood or blood substitute, and a cardioplegia administration tube connected to the downstream ends of the cardioplegia and blood supply tubes; mounting the cardioplegia administration tube in a positive displacement pump for pumping fluid through the cardioplegia administration tube; mounting the cardioplegia and blood supply tubes in pinch valves; and alternately-continually pinching the cardioplegia and blood supply tubes with the pinch valves to close and open the cardioplegia and blood supply tubes such that only one of the cardioplegia and blood supply tubes is open at a time, controlling the intervals during which the pinch valves are open with respect to each of the cardioplegia and blood supply tubes to control the ratio of the cardioplegia medication and blood or blood substitute administered through the cardioplegia administration tube.
The system and method of the present invention allow the composition of the cardioplegia solution to be easily changed without affecting the flow rate, which is determined by the pump. Moreover, the system and method allow the flow rate of cardioplegia solution to be changed without affecting the composition of the solution, which is determined by the controller. Finally, the system and method provide for the delivery of the cardioplegia solution in a closed, sterile pathway. The tubing set can be made to be quickly attached to and removed from the controller and the pump, so that it can be disposed of after use, eliminating the need to clean or sterilize the controller and pump after each use.
These and other features and advantages of the invention will be in part apparent, and in part pointed out hereinafter.